At present, since most high ways are still provided with mixed traffic lanes for cars and trucks, it often occurs that a car while tailgating may hit the back of a truck and result in a traffic accident. Although some trucks have been provided with a flat fender at their rear to protect against car intrusion, it may not achieve the intended purpose of protection against car intrusion due to the fender's inefficiency in resisting impact. Besides, since the fender is fixed to the lower rear of the truck, if an object on a traffic lane is higher than the fixed fender, the object might collide with the fender or the truck, thus causing damage.